welcome to doha , dont worry having rent a car in doha it is like getting vegetables in the market. but i suggest u to get your own car its very cheap, just for 15000 u can afford a luxerious car,u can visit Bn Eid car showroom in Shalwa road just in front of DHL office,to reach there u can hire a karwa taxi which cost only about 15 qr from airport to DHL,i think it is a good suggestion for you.